Continous method of fuel injection in electronically controlled engine

ABSTRACT

The minimum fuel injection time is on electronically controlled fuel injection engine is set in relation to the running condition of the engine. For example, in shift change, when the throttle valve is in the idling angle and the revolution speed of the engine is high, the minimum fuel injection time is set to a small value to improve the efficiency of fuel consumption. Also, at the completion of fuel cut-off when the revolution speed of the engine is low, the minimum fuel injection time is set to a large value to improve the driveability of the vehicle.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a fuel injection method in an electronicallycontrolled engine for calculating fuel injection amounts by the use of amicroprocessor.

2. Description of the Prior Art

In abrupt deceleration or the like, a measuring plate of an air flowmeter produces undershoot, and intake air flow detected from the outputof the air flow meter is remarkably smaller than actual intake air flowso that the fuel injection amount calculated on the basis of the outputof the air flow meter has a very small value, causing a misfire. Thus,to avoid such misfire, the minimum fuel injection amount is determinedand, when the calculated fuel injection amount is smaller than theminimum fuel injection amount, the fuel injection amount is made to bethe minimum fuel injection amount. In the prior fuel injection method,however, the minimum fuel injection amount was constant irrespectivelyof the running condition of an engine. Since the minimum fuel injectionamount capable of avoiding misfire varies with the running condition ofthe engine, when the minimum fuel injection amount is determined so asnot to adversely affect driveability of the vehicle in the prior fuelinjection method, noxious components in exhaust gas increase andefficiency of fuel consumption is degraded under a predetermined runningcondition of the engine. On the other hand, when the minimum fuelinjection amount is determined so as to restrain the noxious amount ofcomponents in the exhaust gas, the driveability is degraded underanother predetermined running condition of the engine.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a fuel injection methodin an electronically controlled engine in which the minimum fuelinjection amount is determined so as to satisfy driveability, fuelconsumption and exhaust emission requirements of a vehicle.

To achieve this object, in the fuel injection method of anelectronically controlled engine constructed according to the presentinvention, the minimum fuel injection amount is set to a firstpredetermined value and then set to a second predetermined value higherthan the first one if the driveability of the vehicle is adverselyaffected when the minimum fuel injection amount has the firstpredetermined value.

Consequently, the minimum fuel injection amount is changed according tothe running condition of the engine so as to maintain the driveabilityupon the resumption of fuel supply after the completion of fuel cut-offwhile restraining noxious components in the exhaust gas and improvingthe efficiency of fuel consumption.

Whether or not the minimum fuel injection amount being set to the firstpredetermined value adversely affects the driveability of the vehicle isdetected from the revolution speed of the engine. For example, when therevolution speed of the engine is lower than a third predeterminedvalue, the minimum fuel injection amount is set to the secondpredetermined value.

Also, whether or not the minimum fuel injection amount being set to thefirst predetermined value adversely affects the driveability of thevehicle is detected, for example, from the revolution speed of theengine and the opening angle of a throttle valve is an intake system.When the revolution speed of the engine is lower than the thirdpredetermined value and the opening angle of the throttle valve in theintake system is at the idling angle, the minimum fuel injection amountis set to the second predetermined value.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of an electronically controlledengine constructed according to the present invention;

FIG. 2 is a block diagram of the electronic control of the engine shownin FIG. 1;

FIG. 3 is a flow chart of an example of a program for executing thismethod;

FIG. 4 is a drawing showing various travelling patterns of anautomobile;

FIGS. 5,6 and 7 are drawings showing changes in fuel injection timeaccording to the cases 1,2 and 3 shown in FIG. 4 respectively; and

FIG. 8 is a flow chart of an example of another program for executingthis method.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Embodiments of the present invention will be described with reference tothe drawings.

FIG. 1 is a schematic illustration of an electronically controlledengine constructed according to the present invention. Air sucked froman air cleaner 1 is sent to a combustion chamber 8 in an engine body 7through an intake path 12 comprising an air flow meter 2, throttle valve3, surge tank 4, intake port 5 and intake valve 6. The throttle valve 3is interlocked with an accelerator pedal 13 in a cab. The combustionchamber 8 is defined by a cylinder head 9, cylinder block 10 and piston11, and exhaust gas produced by combustion of the mixture is purged tothe atmosphere through an exhaust valve 15, exhaust port 16, exhaustmanifold 17 and exhaust pipe 18. A bypass path 21 connects the upstreamside of the throttle valve 3 to the surge tank 4 and a bypass flowcontrolling valve 22 controls the sectional area of flow in the bypasspath 21 to maintain the revolution speed of the engine constant at idle.An exhaust gas recirculation (EGR) path 23 for conducting a part ofexhaust gas to the intake system to restrain the production of nitrogenoxide connects the exhaust manifold 17 to the surge tank 4, and anon-off type exhaust recirculation (EGR) controlling valve 24 opens andcloses the EGR path 23 in response to electric pulses. An intake airtemperature sensor 28 provided in the air flow meter 2 detects intakeair temperature, and a throttle switch 29 detects the idling angle ofthe throttle valve 3. A water temperature sensor 30 mounted on thecylinder block 10 detects coolant temperature, i.e., engine temperatureand an air fuel ratio sensor 31, well known to comprise an oxygenconcentration sensor and mounted on the aggregate portion of the exhaustmanifold 17, detects oxygen concentration in the aggregate portion. Acrank angle sensor 32 detects the crank angle of a crank-shaft (notshown) in the engine body 7 from the rotation of a shaft 34 of adistributor 33 coupled with the crank-shaft, and a vehicle speed sensor35 detects the revolution speed of the output shaft of an automatictransmission 36. The output of these sensors 2,28,29,30,31,32,35 and thevoltage of an accumulator 37 are sent to an electronic control 40. Afuel injection valve 41 is provided respectively near each intake port 5corresponding to each cylinder, and a pump 42 sends fuel to the fuelinjection valve 41 through a fuel path 44 from a fuel tank 43. Theelectronic control 40 calculates the fuel injection amount by using theinputs from the respective sensors as parameters and sends electricpulses having a pulse width corresponding to the calculated fuelinjection amount to the fuel injection valve 41. Also, the electroniccontrol 40 controls the bypass flow controlling valve 22, EGRcontrolling valve 24, and a solenoid 45 in a hydraulic control circuitof automatic transmission 36 and an ignition system 46. The secondaryside of ignition coil in the ignition system 46 is connected to thedistributor 33.

FIG. 2 is a block diagram of the interior of the electronic control. ACPU (Central Processing Unit) 56, a ROM (Read-Only Memory) 57, RAMs(Random Access Memory) 58,59, and an A/D (Analog/Digital) converter 60with a multiplexer and input/output interface 61 are connected to eachother through a bus 62. RAM 59 is connected to an auxiliary power sourceso that it can be hold its memory with a predetermined power suppliedeven in a period when the engine is stopped by opening the ignitionswitch. Analog signals from the air flow meter 2, intake air temperaturesensor 28, water temperature sensor 30 and air fuel ratio sensor 31 aresent to A/D converter 60. The outputs of the throttle switch 29, crankangle sensor 32 and vehicle speed sensor 35 are sent to the input/outputinterface 61, and the bypass flow controlling valve 22, EGR controllingvalve 24, solenoid 45 and ignition system 46 receive the input signalsfrom the input/output interface 61.

FIG. 3 is a flow chart of an example of a program for executing thismethod. Further in an embodiment of the electronically controlledengine, fuel is injected from the respective fuel injection valves onceper cycle of the engine. The fuel injection amount is in proportion tothe fuel injection time. In step 65, whether the throttle switch 29 isturned on or off is determined, and the program proceeds to step 66 ifit is determined to be turned on and to step 68 if it is determined tobe turned off. When the throttle valve 3 is in the idling angle, thethrottle switch 29 is turned on, and when the throttle valve 3 is openedlarger than the idling angle and throttle switch 29 is turned off. Instep 66, it is determined whether or not the revolution speed N of theengine is lower than a predetermined value Na and the program proceedsto step 67 if it is determined to be yes and to step 68 if no. In step67, i.e., when the throttle valve 3 is in the idling angle and therevolution speed N of the engine is lower than the predetermined valveNa, the minimum fuel injection time τmin is set to be τh. The fuelinjection time τh is the fuel injection time like the one upon theresumption of fuel supply after the completion of fuel cut-off, in whichthe minimum fuel injection amount to avoid miss fire corresponds to theminimum fuel injection amount under the running condition of the engine.In step 68, i.e., when the throttle valve 3 has the opening angle largerthan the idling angle or the revolution speed N of the engine is higherthan the predetermined value Na, the minimum fuel injection time τmin isset to be τl (τl<τh). The fuel injecton time τl is the fuel injectiontime corresponding to the minimum fuel injection time under such runningcondition of the engine that the minimum fuel to avoid miss fire isreduced.

FIG. 4 shows various travelling patterns. Na is the minimum revolutionspeed of the engine to start fuel cut-off and equal to Na in step 66 ofFIG. 3. When the revolution speed of the engine is lower than Na, fuelis not cut off even if the engine is under the decelerating condition.Also, Nb is the revolution speed of the engine under which the fuelcut-off is completed. Case 1 is one in which shift change is carried outwhile the revolution speed of the engine is higher than Na. Case 2 isone in which the fuel cut-off is completed and case 3 is one in whichthe engine is brought to the decelerating condition while the revolutionspeed of the engine is lower than Na.

FIG. 5 shows change in the fuel injection time in case 1. At time t1,the throttle valve 3 has the idling angle and at time t2 it is againopened larger than the idling angle. The fuel is not immediately cut offafter the throttle valve 3 has the idling angle, but cut off after apredetermined time elapses. In case 1, since the period of time fromtime t1 to t2 is short, fuel is not cut off, and since the revolutionspeed of the engine is higher than Na, the minimum fuel injection timeis set to τl. Thus, a fuel injection time shorter than τl is allowed sothat noxious components in exhaust gas are reduced and the efficiency offuel consumption is improved.

FIG. 6 shows change in the fuel injection time in case 2. At time t3,the revolution speed of the engine is lower than Nb and the fuelinjection is resumed after the fuel cut-off is completed. In case 2,since the revolution speed of the engine is lower than Na the minimumfuel injection time τmin is set to τh without causing any misfire toensure a predetermined engine output, i.e., driveability of the vehicle.The broken line shows the fuel injection time in the prior methodsetting the minimum fuel injection time always to τl irrespective of therunning condition of the engine. According to the prior method, noxiouscomponent amount in exhaust gas is to be restrained to provide asatisfactory result in case 1, but in case 2 a misfire may be causedthus adversely affecting the driveability of the vehicle.

FIG. 7 shows change in the fuel injection time of case 3. The engine isunder the decelerating condition in time t4. In case 3, since therevolution speed of the engine is lower than Na, the minimum fuelinjection time τmin is set to τh. Thus, a misfire is not caused, but apredetermined engine output (i.e., the driveability of the vehicle) isensured.

FIG. 8 is a flow chart of an example of another program for excutingthis method. In step 71, it is determined whether or not the revolutionspeed N of the engine is lower than the predetermined value Na, and theprogram proceeds to step 72 if it is determined to be yes and to step 73if no. In step 72, i.e., when the revolution speed N of the engine islower than Na, the minimum fuel injection time τmin is set to τh. Instep 73, i.e., when the revolution speed N of the engine is higher thanthe predetermined value Na, the minimum fuel injection time τmin is setto τl. Thus, under the running condition of the engine in which theminimum fuel injection time to avoid misfire increases, the minimum fuelinjection time τmin is set to large value τh and hindrances to thedriveability are avoided. Under the running condition of engine in whichthe minimum fuel injection to avoid misfire decreases, the minimum fuelinjection time τmin is set to small value τl and thereby the noxiouscomponents in the exhaust gas can be restrained. In the embodiment shownin FIG. 8, a step corresponding to the step 65 in FIG. 3 is omitted tosimplify the program.

What is claimed is:
 1. A method for fuel injection in a vehicle with anelectronically controlled engine having a calculated fuel injectionamount and a minimum fuel injection amount, the minimum fuel injectionamount, in the absence of fuel cut-off, being supplied to the enginewhen the calculated fuel injection amount is less than the minimum fuelinjection amount, said method comprising the steps of:setting theminimum fuel injection amount to a first predetermined value; andsetting the minimum fuel injection amount to a second predeterminedvalue higher than said first predetermined value whenever driveabilityof the vehicle is adversely affected by the setting of the minimum fuelinjection amount to said first predetermined value.
 2. A method asrecited in claim 1 wherein an adverse effect on the driveability of thevehicle is detected from the revolution speed of the engine.
 3. A methodas recited in claim 2, wherein the minimum fuel injection amount is setto said first predetermined value when the revolution speed of theengine is higher than a third predetermined value, and the minimum fuelinjection amount is set to said second predetermined value when therevolution speed of the engine is lower than said third predeterminedvalue.
 4. A method as recited in claim 1 wherein an adverse effect ondriveability of the vehicle is detected from the revolution speed of theengine and the opening angle of a throttle valve in the intake system ofthe engine.
 5. A method as recited in claim 4 wherein the minimum fuelinjection amount is set to said first predetermined value when therevolution speed of the engine is higher than a third predeterminedvalue or when the throttle value is not at the idling angle; and whereinthe minimum fuel injection amount is set to said second predeterminedvalue when the revolution speed of the engine is lower than the thirdpredetermined value and the throttle valve is at the idling angle.
 6. Amethod for fuel injection in a vehicle with an electronically controlledengine having a calculated fuel injection pulse width and a minimum fuelinjection pulse width, the minimum fuel injection pulse width, in theabsence of fuel cut-off, being supplied to the engine when thecalculated fuel injection pulse width is less than the minimum fuelinjection pulse width, said method comprising the steps of:setting theminimum fuel injection pulse width to a first predetermined value; andsetting the minimum fuel injection pulse width to a second predeterminedvalue higher than said first predetermined value whenever driveabilityof the vehicle is adversely affected by the setting of the minimum fuelinjection pulse width to said first predetermined value.
 7. A method asrecited in claim 6 wherein an adverse effect on the driveability of thevehicle is detected from the revolution speed of the engine.
 8. A methodas recited in claim 7 wherein the minimum fuel injection pulse width isset to said first predetermined value when the revolution speed of theengine is higher than a third predetermined value, and the minimum fuelinjection pulse width is set to said second predetermined value when therevolution speed of the engine is lower than said third predeterminedvalue.
 9. A method as recited in claim 6 wherein an adverse effect ondriveability of the vehicle is detected from the revolution speed of theengine and the opening angle of a throttle valve in the intake system ofthe engine.
 10. A method as recited in claim 9 wherein the minimum fuelinjection pulse width is set to said first predetermined value when therevolution speed of the engine is higher than a third predeterminedvalue or when the throttle valve is not at the idling angle; and whereinthe minimum fuel injection pulse width is set to said secondpredetermined value when the revolution speed of the engine is lowerthan said third predetermined value and the throttle valve is at theidling angle.